Much piping through which high-temperature water and low-temperature water flow is provided in plants such as nuclear power plants and thermal power plants. Such piping includes a branch pipe perpendicularly connected to a main pipe and has a fluid-mixing region where low-temperature water flowing through the branch pipe joins high-temperature water flowing through the main pipe (of course, a configuration in which low-temperature water flows through the main pipe and high-temperature water flows through the branch pipe is also possible). In the fluid-mixing region, a temperature interface is formed between the high-temperature water and the low-temperature water. This temperature interface varies in position (temperature fluctuation), thus causing the problem that the metal constituting the piping experiences thermal fatigue. To avoid the thermal fatigue, the high-temperature water and the low-temperature water must be quickly mixed.
Patent Document 1 discloses a technique for facilitating the mixing of high-temperature water flowing through a main pipe and low-temperature water flowing out of a reducer through a branch pipe by fixing an upstream end of the reducer to an inner circumferential wall of the branch pipe and positioning a downstream end of the reducer, having a reduced inner diameter, on the central axis of the main pipe.
Also disclosed is a technique for further facilitating the mixing of the fluids by providing guide vanes on the reducer disposed inside the main pipe to apply a swirling force to the fluid flowing through the main pipe.
Patent Document 1: Japanese Unexamined Patent Application, Publication No. 2005-16686 (FIGS. 10, 13, and 14)